Re: [igt-dev] [PATCH v6 03/13] fb: Create common function to convert frame formats

[Maxime Ripard <maxime.ripard@bootlin.com>]

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On Fri, Aug 31, 2018 at 04:41:10PM +0300, Ville Syrjälä wrote:
> On Fri, Aug 31, 2018 at 03:12:12PM +0200, Maxime Ripard wrote:
> > The current code to convert between two buffer formats is quite tied to the
> > cairo surface infrastructure. Since we'll want to reuse it, make that
> > function more generic by introducing a common structure that passes all the
> > arguments and a common function that will call the right functions we
> > needed.
> > 
> > Reviewed-by: Eric Anholt <eric@anholt.net>
> > Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
> > ---
> >  lib/igt_fb.c | 243 ++++++++++++++++++++++++++++++++--------------------
> >  1 file changed, 153 insertions(+), 90 deletions(-)
> > 
> > diff --git a/lib/igt_fb.c b/lib/igt_fb.c
> > index 4061fedec0c1..1914233786a5 100644
> > --- a/lib/igt_fb.c
> > +++ b/lib/igt_fb.c
> > @@ -1384,6 +1384,24 @@ struct fb_convert_blit_upload {
> >  	struct fb_blit_linear linear;
> >  };
> >  
> > +struct fb_convert_buf {
> > +	void			*ptr;
> > +	unsigned int		stride;
> > +	unsigned int		size;
> > +	uint32_t		fmt;
> > +	enum igt_color_encoding	color_encoding;
> > +	enum igt_color_range	color_range;
> > +	uint32_t		offsets[4];
> > +};
> 
> I wonder if we can just use igt_fb for that instead of duplicating most
> of it?

After looking into it again, now I remember why I didn't do what you
suggested. In the case where you are in the YUYV path, with a "shadow"
buffer being used to perform the cairo operations on top of an YUV
buffer, you end up with conversions in create_cairo_surface__convert
and destroy_cairo_surface__convert, getting a fb_convert_blit_upload
structure as an argument.

That structure however is used to convert one buffer to the shadow
buffer, or the other way around at destroy time. However, a single
igt_fb is allocated for that structure, which makes it impossible to
assign the second fb in that particular case. All the informations
needed to perform the conversion are stored in multiple structures
(fb_convert_blit_upload.linear, fb_convert_blit_upload.blit, and the
actual igt_fb instance) that we need to aggregate to find the correct
conversion parameters.

Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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